1. Field of the Invention
The present invention relates to an enzymatic process for converting maleic acid to fumaric acid, characterized in that the lifetime of the enzyme used in the converting reaction is extended by lowering dissolved oxygen concentrations in the medium for the substrate. In addition, the present invention relates to a enzymatic process for producing L-aspartic acid by reacting maleic acid with ammonium, characterized in that the lifetime of the enzyme used in the reaction is extended by lowering the dissolved oxygen concentration in the medium for the substrate.
2. Related Art
It has been found out that the microorganisms that belong to genera of Pseudomonas, Bacillus, Aeobacter (Enterobacter) or Brervibacterium can convert maleic acid to fumaric acid (sees for example, Japanese Examined Patent Publication No. 42-11993, and Japanese Examined Patent Publication No. 42-11994). In general, in an enzymatic reaction, using an enzyme for a certain period of time necessitates exchanges of the enzyme due to inactivation of the enzyme. Such an inactivation is inevitable because of the fact that an enzyme is a proteinacious material. In particular, in the process for producing L-aspartic acid by reacting maleic acid with ammonium, the maleic acid-isomerizing enzyme used is prone to be inactivated by oxygen, therefore, the enzyme has to be exchanged quite frequently. A non-batch process using such an enzyme causes the cost of the facilities and the personnel to be high.